In the manufacture of motorcar bodies and parts it is absolutely usual to operate with fastener elements which are present in the form of rivet elements, piercing elements or press-in elements.
With a rivet element the element is inserted into a pre-pierced sheet metal part and riveted to the sheet metal part by beading over the rivet section of the fastener element. The fastener element itself has a fastener part, i.e. either an internal thread or a bolt shaft with an external thread, whereby a further component can be secured to the sheet metal part using a bolt or a nut respectively. Piercing elements, which can be formed either as rivet elements or press-in elements are termed self-piercing elements i.e. the element itself cuts a hole in the sheet metal part and is subsequently secured to the sheet metal part. With the known press-in elements the sheet metal part can be pre-pierced or the press-in element can, as indicated above, be made in self-piercing manner, i.e. so that an attachment to a sheet metal part itself cuts a hole in the sheet metal part under the forces that are applied. The element is passed through the hole and the sheet metal part is pressed so that sheet metal material flows into undercuts of the press-in element. The press-in element is thus locked to the sheet metal part in this way so that it is securely fastened to the sheet metal part and cannot be straightforwardly pressed axially out of the sheet metal part or rotated relative to the sheet metal part with the usual torques which arise on attaching a bolt or a nut. Press-in elements are, in contrast to rivet elements, not deformed on attachment to the sheet metal part or essentially not intentionally deformed.
Such fastener elements have generally replaced the weld elements in the construction of motor vehicles which were previously welded to sheet metal bodywork and the like. The welding on of elements can, on the one hand, only be poorely integrated into the process of manufacture of individual sheet metal parts by mechanical deformation and leads also to an undesired contamination of the sheet metal part. Furthermore weld elements cannot be used with diverse sheet metal parts such as, for example, sheet metal parts which are pre-painted or which consist of two sheet metal layers, optionally with a plastic membrane disposed between them. They can also not be used when the sheet metal part is a high strength sheet metal part since the heat which arises during the welding leads to an unacceptable reduction of the characteristics of the sheet metal in the region of the weld position. In the manufacture of sheet metal parts for motor vehicles large numbers are required and the sheet metal thicknesses which enter into question normally lie in the range from 0.6 mm to 2.5 mm, occasionally beyond this up to 3 mm or somewhat more.
DE 10 2007 034 987 A1 describes a press-in element which can be formed as self-piercing element and which is suitable for attachment in thick sheet metal parts. The press-in element shown there has a head part having a ring surface confronting the sheet metal part and a neck part which projects away from the ring surface i.e. away from the sheet metal contact surface, with the head part furthermore having a ring shaped projection surrounding the neck part with a radial spacing and projecting away from the ring surface. The neck part also has a radially outwardly projecting ring bead which can be formed as a continuous ring bead and also as a locally interrupted ring bead. The tip of the bead has an axial spacing from the ring surface which is larger than the axial spacing of the tip of the ring-shaped projection from the ring surface. The ring bead lies radially within this projection and forms with the latter a pocket which takes up material of the sheet metal part. A press-in element of this kind certainly has its justification but is however relatively complicated in its manufacture. Furthermore, the design in the region of the ring surface and directly below the ring surface at the neck part can under some circumstances lead to greater difficulties during the attachment of the sheet metal part as the desired form-fitted locking which aimed at with the sheet metal part cannot be ensured under some circumstances to the desired level.
At this point reference should be made also the European patent EP-B-1 690 913. Here a further functional element is described which has a sheet metal contact surface of ring shape at the underside of a head part and a neck part projecting away from the latter which is here designed as a piercing section. This functional element is characterized in that it can be used with sheet metal parts of various thicknesses. For this purpose a ring-like bead is provided at the piercing section between the ring-like sheet metal contact surface and the free end of the piercing section and furthermore a ring recess is provided between the bead and the free end of the piercing section around the piercing section. In addition, ribs providing security against rotation are provided which extend in raised manner within a further ring groove between the sheet metal contact surface and the bead in the axial direction up to the bead. An element of this kind is entirely able to satisfy its task is however relatively complicated and is also not well suited to be used in a self-piercing manner in really thick sheet metal parts in the range from 4 mm thickness and above.
In EP-B-1 690 013 it is brought out that the element can be used with sheet metal thickness in the range between 0.6 mm and 4 mm, with sheet metal thickness above 3 mm being relatively rare in motorcar construction. Fastener elements are however also used in the manufacture of trucks but to a much smaller degree. Essentially it is only the use of rivet elements from the manufacture of motorcars which is known. These are also used in thinner sheet metal parts in trucks, for example in the area of the driver's cabin. More stable sheet metal parts of a truck, i.e. with sheet metal thicknesses greater than 3 mm and usually greater than 4 mm and even larger are—if at all—only provided in the rarest cases with rivet elements because the available rivet elements are simply not designed for such thick sheet metal parts. Furthermore, many fewer trucks are manufactured in comparison to motorcars. In the manufacture of trucks, weld elements are currently been used to a large extent.